Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é o resultado de 1991 para os Grand Slams de 1993?
 ###Tabelas: CREATE TABLE season_5_2008–09 (season_5_2008–09_id AUTO_INCREMENT PRIMARY KEY, Series # INT, Season # INT, Title VARCHAR, Directed by VARCHAR, Written by VARCHAR, Original air date VARCHAR, Production code INT) CREATE TABLE historical (historical_id AUTO_INCREMENT PRIMARY KEY, Begin Date VARCHAR, Representative VARCHAR, Date of birth VARCHAR, House term VARCHAR, State served VARCHAR, Party VARCHAR, Age (years, days) VARCHAR) CREATE TABLE singles_performance_timeline (singles_performance_timeline_id AUTO_INCREMENT PRIMARY KEY, Tournament VARCHAR, 1990 VARCHAR, 1991 VARCHAR, 1992 VARCHAR, 1993 VARCHAR, 1994 VARCHAR, 1995 VARCHAR, 1996 VARCHAR, 1997 VARCHAR, 1998 VARCHAR, 1999 VARCHAR, 2000 VARCHAR, 2001 VARCHAR, Career SR VARCHAR, Career Win-Loss VARCHAR) CREATE TABLE asian_youth_games (asian_youth_games_id AUTO_INCREMENT PRIMARY KEY, Sport VARCHAR, Gold INT, Silver INT, Bronze INT, Total INT) CREATE TABLE internal_correspondences (internal_correspondences_id AUTO_INCREMENT PRIMARY KEY, Tongan VARCHAR, Niuean VARCHAR, Sāmoan VARCHAR, Takuu VARCHAR, Tahitian VARCHAR, Rarotongan VARCHAR, Māori VARCHAR, North Marquesan VARCHAR, South Marquesan VARCHAR, Hawai'ian VARCHAR, Mangarevan VARCHAR)  
SELECT 1991 FROM singles_performance_timeline WHERE 1993 = grand slams